The invention relates to multi-layer elastic thermoplastic films, which consist of at least one layer of thermoplastic polyurethane (TPE-U), at least one further layer of thermoplastic polyurethane which is blended with modified acrylonitrile-butadiene-styrene copolymer (MABS), and optionally at least one support layer of thermoplastic polymer which is incompatible with TPE-U, and to the use thereof, in particular for the water-tight and breathable sealing of fabrics, such as wovens and non-wovens, and the everyday objects produced therefrom, in particular in the clothing sector and in the medical wound covering sector.
It is known that the clothing sector and the medical sector can be served with films of cast polyurethane. Owing to the specific properties of cast polyurethane, a relatively expensive matted release liner is necessary here. Moreover, the polyurethane is cast from reactive dispersions which still have to cure fully, and there is the risk that low molecular weight residual components may remain if the process is not carried out properly. These low molecular weight components often display migration tendencies, which means that these films are no longer acceptable for applications in direct contact with skin. In addition, they are not hard-wearing and are therefore unusable.
It is also known that pore-free films with high water vapour permeability, as described e.g. in EP-A 0 591 782, are used. In EP-A 0 658 581, the use of hydrophilic TPE-Us in the sector of breathable textile fabrics is described.
A review of the group of the thermoplastic elastomers is provided by, for example:
Thermoplastic elastomers; a comprehensive review, ed. N. R. Legge, G. Holden and H. E. Schroeder, Carl Hanser Verlag, Munich, 1987 and Thermoplastische Elastomere—Herausforderung an die Elastomerverarbeiter, ed.: VDI-Gesellschaft Kunststofftechnik, VDI Verlag, Düsseldorf, 1997.
The use of hydrophilic TPE-Us for wound coverings is described e.g. in U.S. Pat. No. 4,614,183 or EP-A 0 714 950. The systems described there have the disadvantage that they achieve adequate slip behaviour only through the addition of large proportions of lubricants and anti-blocking agents. TPE-U structures optimised in terms of their water vapour permeability by coextrusion are known, for example from WO 99/38927 A1. The coextrudates of hydrophilic TPE-Us described there with different Shore-A hardnesses or different soft segment proportions likewise fail to exhibit adequate slip behaviour without the addition of large proportions of lubricants and anti-blocking agents.
Single-layer films of TPE-U, methods for their production and their use are known, for example from EP-A 0 308 683, EP-A 0 526 858, EP-A 0 571 868 or EP-A 0 603 680. The films described in these documents can be integrated as layers into so-called laminating films or have already been integrated into the laminating films that are known per se. The production of TPE-U films using substantially incompatible polymers as matting agents in TPE-U is also described e.g. in DE-A 41 26 499.
Multi-layer films produced by coextrusion from TPE-U and other polymers belonging to the group of the thermoplastics are also known. As well as coextrusion with polyolefinic thermoplastics, in which the polyolefinic layer generally has no composite adhesion with the TPE-U layer and only possesses the function of a support or release layer, multi-layer structures with good composite adhesion are also known. In EP-A 0 842 768, for example, a multi-layer structure of TPE-U and a polyolefinic adhesion promoter is described.
The reduction of the blocking behaviour of thermoplastic TPE-U by polystyrene is known, e.g. from EP-A 0 754 543. US-A 2006/0189754 describes a method for the production of compounded, transparent material mixtures and thick-walled articles with good slip properties made thereof In US-A 2006/0189754, mixtures containing up to 50% modified acrylonitrile-butadiene-styrene copolymer (MABS) in TPE-U were used. These articles have the disadvantage of low mechanical load-bearing capacity owing to the incompatibility of the components described. The articles according to US-A 2006/0189754 therefore utilise penetrable substrates as support material.
TPE-U films according to the prior art normally additionally contain common additives from the group comprising:
I. inorganic or organic anti-blocking agents,
II. lubricants or mould release agents,
III. pigments or fillers and
IV. stabilizers.
The proportion of the above additives Ito IV is, in total, preferably between 0 wt. % and 30 wt. %, based on the film.
The most common additives, which can also be contained in the films according to the invention described below, are described for example by Gächter and Müller in: Plastics Additives, Carl Hanser Verlag Munich, 4th edition (1996).